1. Field of the Invention
The present invention applies to a structure for a frame used in communications between base stations and user terminals and, in particular, to a frame structure that includes uplink and downlink slots in a time division format.
2. Description of the Prior Art
Time division mobile radio communications systems such as cellular data and voice radio systems typically use a repeating frame that includes slots allocated for specific purposes. In a frequency division TDD (Time Division Multiple Access) system, the repeating frame may include a set of downlink slots. The uplink slots are in a different frame on a different frequency. Broadcast, random access and control channel messages may each be assigned to specific frequencies that use a different frame structure. Each frame type can be optimized for the type of messages that it carries enhancing efficiency. In a TDD (Time Division Duplex) system, uplink and downlink slots are in the same frame. In some instances, specific slots within the frame may carry some control messages. However, the control and access channels are normally in separate frames.
Separate broadcast, control, and access channels allow great flexibility in designing a wireless radio network of base stations and remote user terminals. However, each channel that is set aside for broadcast, control, or access purposes cannot be used for traffic. When the number of channels is limited in comparison to the demand for traffic, it is preferred to maximize the traffic usage of all of the system's radio capacity. Combining different functions into a single frame, on the other hand, makes interference between neighboring slots likely. It also can restrict variations in the comparative data rate between uplink and downlink.